As the semiconductor element becomes higher in integration or performance, it is becoming more difficult to make failure analysis in the semiconductor element. To facilitate such failure analysis of semiconductor elements, if only to a lesser extent, a wide diversity of techniques for analysis of failures of the semiconductor elements has so far been developed. As one of the techniques for failure analysis of semiconductor elements, there is known a technique of discriminating a failure with an electron beam failure analysis device in accordance with a potential contrast method.
In this method, the surface of an electrically conductive layer (wiring, interconnect or vias) of a semiconductor element is exposed by e.g., polishing. The surface of the semiconductor element is then charged to a desired charging potential. The electrically conductive layer exposed is irradiated with an electron beam, and secondary electrons emitted from the semiconductor element are observed with the scanning electron microscope (SEM) to obtain a potential contrast image. In case an open failure or a shortage failure exists below the electrically conductive layer being observed, the potential contrast image obtained yields different contrast as compared to an image that may be obtained with a regular semiconductor element.
However, the method that uses such electron beam failure analysis apparatus to acquire potential contrast images of a failed semiconductor element and a regular semiconductor element by a potential contrast method to compare these two in order to detect non-coincident portions is premised on the presence of the regular semiconductor element. It is not possible to identify a failed site in case none of the semiconductor elements has been manufactured as designed such that there is no regular device or in case a semiconductor element that may be used as comparison reference has not been produced because of operational failures brought about incidentally. For such case, there has been proposed a method of generating a pseudo-regular picture image from design data to compare it to an image of secondary electrons as an object being analyzed.
Patent Document 1, for example, discloses an automatic inspection system for an X-ray mask etc. In the inspection system, an electron beam is irradiated to an electrically conductive substrate, and one out of secondary electrons generated, reflected electrons and transmitted electrons is detected. Picture images obtained from so generated electron signals are compared to one another to automatically locate the failures. There are proposed die-to-die inspection that compares picture images derived from the dies to each other and a die-to-database inspection that compares a picture image derived from the die and a picture image generated by a picture image simulator that has input CAD data of the die (pseudo-regular picture image).
Patent Document 2 discloses detecting and deciding a failure or foreign matter, according to which a semiconductor wafer being inspected is put on a sample stand of an electron microscope and an electron beam is irradiated to an inspection area on the major surface of the semiconductor wafer. The inspection area represents an object of inspection. By so doing, secondary electrons and reflected electrons are generated and detected respectively by a secondary electron detector and by a reflected electron detector. A detection signal converter, a picture image write/display circuit, a comparison calculation circuit and a failure determining processing circuit are then in operation to detect and identify failures or foreign matter.
In the method of Patent Document 1, according to which a pseudo-regular picture image is generated from design data and compared to an image of secondary electrons being analyzed, it is difficult to compare the images of secondary electrons, observed in a device for analysis, such as SEM, with the pseudo-regular picture image. The images of secondary electrons, observed in general in a device for analysis, such as SEM, are difficult to compare to the picture image of the pseudo-regular picture image on account of the difference in shape and scale size from the design data. It may be said that miniaturization of the semiconductor element, now going on at large, may account for such difficulty. With this in view, there are disclosed methods in Patent Documents 3 and 4 for generating a pseudo-regular picture image from an image of secondary electrons of the semiconductor element.
In Patent Document 3, an image of secondary electrons, obtained on irradiating a semiconductor element with a beam of charged particles, is fractionated into a plurality of different potential regions and, using design data, potential concentration distributions of the respective regions are calculated. The respective regions of the image of secondary electrons are colored to different hues in accordance with the potential regions to generate a pseudo-regular secondary electron image. The pseudo-regular secondary electron image and the secondary electron image being analyzed are displayed. In Patent Document 3, the potential contrast image is fractionated into a plurality of different potential regions. Then, using design data, the potential concentration distributions of the respective regions, corresponding to luminosity or contrast in the contrast image, are calculated.
In Patent Document 4, the secondary electron image, obtained on irradiating the semiconductor element with a beam of charged particles, is fractionated into a plurality of different potential regions. The concentrations of the respective regions are smoothed by carrying out smoothing processing to generate a pseudo-regular secondary electron image. The pseudo-regular secondary electron image and the secondary electron image being analyzed are displayed.
FIG. 18 depicts a block diagram of the device for analysis shown in Patent Document 4. A SEM image inputting means 10 inputs secondary electrons from a SEM device. The secondary electrons have been obtained on irradiating the semiconductor element with a beam of charged particles. A potential-based fractionating means 12 fractionates the secondary electron image, input to the SEM image inputting means 10, into a plurality of potential-based regions, using design data of the semiconductor element stored in a design data memory means 16 as reference. The potential concentrations are smoothed by a region-based smoothing means 14 from one potential-based region to another. In more concrete terms, the potential contrast is varied depending on different types of connection destinations of the wiring (interconnects), such as P+ diffusion, N+ diffusion or Poly-Si, as disclosed in paragraph [0014] of Patent Document 4.
Non-Patent Document 1 shows canny edge detection. Though not directly relevant to failure analysis of semiconductor elements, this canny edge detection is a method for object contour detection well-known in the field of computational picture image processing. It is generally accepted that the canny edge detection is featured by low error rates in edge extraction, high edge position detection accuracy and detection of a single edge per edge region.    [Patent Document 1] JP Patent Kokai Publication No. JP-A-5-258703    [Patent Document 2] JP Patent Kokai Publication No. JP-P2006-286685A    [Patent Document 3] JP Patent Kokai Publication No. JP-P2009-231490A    [Patent Document 4] JP Patent Kokai Publication No. JP-P2009-252414A    [Non-Patent Document 1] J. Canny: “A Computational Approach to Edge Detection”, IEEE Trans. On Pattern Analysis and Machine Intelligence, 8(6), pp. 679 to 698, November 1986